History
Technical details
A PDF file is often a combination ofPostScript language
if
statements and loop
commands. PDF is largely based on PostScript but simplified to remove flow control features like these, while graphics commands equivalent to lineto
remain.
Historically, the PostScript-like PDF code is generated from a source PostScript file. The graphics commands that are output by the PostScript code are collected and tokenized. Any files, graphics, or fonts to which the document refers also are collected. Then, everything is compressed to a single file. Therefore, the entire PostScript world (fonts, layout, measurements) remains intact.
As a document format, PDF has several advantages over PostScript:
* PDF contains tokenized and interpreted results of the PostScript source code, for direct correspondence between changes to items in the PDF page description and changes to the resulting page appearance.
* PDF (from version 1.4) supports transparent graphics; PostScript does not.
* PostScript is an File format
A PDF file is organized using%PDF-1.7
. The format is a subset of a COS ("Carousel" Object Structure) format. A COS tree file consists primarily of ''objects'', of which there are nine types:
* (...)
) or represented as hexadecimal within single angle brackets (<...>
). Strings may contain 8-bit characters.
* Names, starting with a forward slash (/
)
* Arrays, ordered collections of objects enclosed within square brackets ( ../code>)
* Dictionaries
A dictionary is a listing of lexemes from the lexicon of one or more specific languages, often arranged alphabetically (or by radical and stroke for ideographic languages), which may include information on definitions, usage, etymologies, p ...
, collections of objects indexed by names enclosed within double angle brackets (<<...>>
)
* Streams
A stream is a continuous body of water, body of surface water Current (stream), flowing within the stream bed, bed and bank (geography), banks of a channel (geography), channel. Depending on its location or certain characteristics, a stream ...
, usually containing large amounts of optionally compressed binary data, preceded by a dictionary and enclosed between the stream
and endstream
keywords.
* The null object
Furthermore, there may be comments, introduced with the percent sign (%
). Comments may contain 8-bit characters.
Objects may be either ''direct'' (embedded in another object) or ''indirect''. Indirect objects are numbered with an ''object number'' and a ''generation number'' and defined between the obj
and endobj
keywords if residing in the document root. Beginning with PDF version 1.5, indirect objects (except other streams) may also be located in special streams known as ''object streams'' (marked /Type /ObjStm
). This technique enables non-stream objects to have standard stream filters applied to them, reduces the size of files that have large numbers of small indirect objects and is especially useful for ''Tagged PDF''. Object streams do not support specifying an object's ''generation number'' (other than 0).
An index table, also called the cross-reference table, is located near the end of the file and gives the byte offset of each indirect object from the start of the file. This design allows for efficient random access
Random access (more precisely and more generally called direct access) is the ability to access an arbitrary element of a sequence in equal time or any datum from a population of addressable elements roughly as easily and efficiently as any othe ...
to the objects in the file, and also allows for small changes to be made without rewriting the entire file (''incremental update''). Before PDF version 1.5, the table would always be in a special ASCII format, be marked with the xref
keyword, and follow the main body composed of indirect objects. Version 1.5 introduced optional ''cross-reference streams'', which have the form of a standard stream object, possibly with filters applied. Such a stream may be used instead of the ASCII cross-reference table and contains the offsets and other information in binary format. The format is flexible in that it allows for integer width specification (using the /W
array), so that for example, a document not exceeding 64 KiB
The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable unit ...
in size may dedicate only 2 bytes for object offsets.
At the end of a PDF file is a footer containing
* The startxref
keyword followed by an offset to the start of the cross-reference table (starting with the xref
keyword) or the cross-reference stream object, followed by
* The %%EOF
end-of-file marker.
If a cross-reference stream is not being used, the footer is preceded by the trailer
keyword followed by a dictionary containing information that would otherwise be contained in the cross-reference stream object's dictionary:
* A reference to the root object of the tree structure, also known as the ''catalog'' (/Root
)
* The count of indirect objects in the cross-reference table (/Size
)
* Other optional information
Within each page, there are one or multiple content streams that describe the text, vector and images being drawn on the page. The content stream is stack-based
Stack-oriented programming, is a programming paradigm which relies on a stack machine model for passing parameters. Stack-oriented languages operate on one or more stacks, each of which may serve a different purpose. Programming constructs i ...
, similar to PostScript
PostScript (PS) is a page description language in the electronic publishing and desktop publishing realm. It is a dynamically typed, concatenative programming language. It was created at Adobe Systems by John Warnock, Charles Geschke, Doug Br ...
.
There are two layouts to the PDF files: non-linearized (not "optimized") and linearized ("optimized"). Non-linearized PDF files can be smaller than their linear counterparts, though they are slower to access because portions of the data required to assemble pages of the document are scattered throughout the PDF file. Linearized PDF files (also called "optimized" or "web optimized" PDF files) are constructed in a manner that enables them to be read in a Web browser plugin without waiting for the entire file to download, since all objects required for the first page to display are optimally organized at the start of the file. PDF files may be optimized using Adobe Acrobat
Adobe Acrobat is a family of application software and Web services developed by Adobe Inc. to view, create, manipulate, print and manage Portable Document Format (PDF) files.
The family comprises Acrobat Reader (formerly Reader), Acrobat (forme ...
software or QPDF.
Imaging model
The basic design of how graphics
Graphics () are visual images or designs on some surface, such as a wall, canvas, screen, paper, or stone, to inform, illustrate, or entertain. In contemporary usage, it includes a pictorial representation of data, as in design and manufacture ...
are represented in PDF is very similar to that of PostScript
PostScript (PS) is a page description language in the electronic publishing and desktop publishing realm. It is a dynamically typed, concatenative programming language. It was created at Adobe Systems by John Warnock, Charles Geschke, Doug Br ...
, except for the use of transparency, which was added in PDF 1.4.
PDF graphics use a device-independent Cartesian coordinate system
A Cartesian coordinate system (, ) in a plane is a coordinate system that specifies each point uniquely by a pair of numerical coordinates, which are the signed distances to the point from two fixed perpendicular oriented lines, measured in t ...
to describe the surface of a page. A PDF
Portable Document Format (PDF), standardized as ISO 32000, is a file format developed by Adobe in 1992 to present documents, including text formatting and images, in a manner independent of application software, hardware, and operating systems. ...
page description can use a matrix
Matrix most commonly refers to:
* ''The Matrix'' (franchise), an American media franchise
** ''The Matrix'', a 1999 science-fiction action film
** "The Matrix", a fictional setting, a virtual reality environment, within ''The Matrix'' (franchis ...
to scale, rotate
Rotation, or spin, is the circular movement of an object around a '' central axis''. A two-dimensional rotating object has only one possible central axis and can rotate in either a clockwise or counterclockwise direction. A three-dimensional ...
, or skew
Skew may refer to:
In mathematics
* Skew lines, neither parallel nor intersecting.
* Skew normal distribution, a probability distribution
* Skew field or division ring
* Skew-Hermitian matrix
* Skew lattice
* Skew polygon, whose vertices do not ...
graphical elements. A key concept in PDF is that of the ''graphics state'', which is a collection of graphical parameters that may be changed, saved, and restored by a ''page description''. PDF has (as of version 2.0) 25 graphics state properties, of which some of the most important are:
* The ''current transformation matrix'' (CTM), which determines the coordinate system
* The ''clipping path
A clipping path (or "deep etch") is a closed vector path, or shape, used to cut out a 2D image in image editing software. Anything inside the path will be included after the clipping path is applied; anything outside the path will be omitted fro ...
''
* The ''color space
A color space is a specific organization of colors. In combination with color profiling supported by various physical devices, it supports reproducible representations of colorwhether such representation entails an analog or a digital represent ...
''
* The '' alpha constant'', which is a key component of transparency
*''Black point compensation Black point compensation is a technique used in digital photography printing
Printing is a process for mass reproducing text and images using a master form or template. The earliest non-paper products involving printing include cylinder seals ...
'' control (introduced in PDF 2.0)
Vector graphics
As in PostScript
PostScript (PS) is a page description language in the electronic publishing and desktop publishing realm. It is a dynamically typed, concatenative programming language. It was created at Adobe Systems by John Warnock, Charles Geschke, Doug Br ...
, vector graphics
Vector graphics is a form of computer graphics in which visual images are created directly from geometric shapes defined on a Cartesian plane, such as points, lines, curves and polygons. The associated mechanisms may include vector display a ...
in PDF are constructed with ''paths''. Paths are usually composed of lines and cubic Bézier curve
A Bézier curve ( ) is a parametric curve used in computer graphics and related fields. A set of discrete "control points" defines a smooth, continuous curve by means of a formula. Usually the curve is intended to approximate a real-world shape t ...
s, but can also be constructed from the outlines of text. Unlike PostScript
PostScript (PS) is a page description language in the electronic publishing and desktop publishing realm. It is a dynamically typed, concatenative programming language. It was created at Adobe Systems by John Warnock, Charles Geschke, Doug Br ...
, PDF does not allow a single path to mix text outlines with lines and curves. Paths can be stroked, filled, fill then stroked, or used for clipping. Strokes and fills can use any color set in the graphics state, including ''patterns''. PDF supports several types of patterns. The simplest is the ''tiling pattern'' in which a piece of artwork is specified to be drawn repeatedly. This may be a ''colored tiling pattern'', with the colors specified in the pattern object, or an ''uncolored tiling pattern'', which defers color specification to the time the pattern is drawn. Beginning with PDF 1.3 there is also a ''shading pattern'', which draws continuously varying colors. There are seven types of shading patterns of which the simplest are the ''axial shading'' (Type 2) and ''radial shading'' (Type 3).
Raster images
Raster images in PDF (called ''Image XObjects'') are represented by dictionaries with an associated stream. The dictionary describes the properties of the image, and the stream contains the image data. (Less commonly, small raster images may be embedded directly in a page description as an ''inline image''.) Images are typically ''filtered'' for compression purposes. Image filters supported in PDF include the following general-purpose filters:
* ''ASCII85Decode'', a filter used to put the stream into 7-bit ASCII
ASCII ( ), abbreviated from American Standard Code for Information Interchange, is a character encoding standard for electronic communication. ASCII codes represent text in computers, telecommunications equipment, and other devices. Because of ...
,
* ''ASCIIHexDecode'', similar to ASCII85Decode but less compact,
* ''FlateDecode'', a commonly used filter based on the deflate algorithm defined in (deflate is also used in the gzip, PNG, and zip
Zip, Zips or ZIP may refer to:
Common uses
* ZIP Code, USPS postal code
* Zipper or zip, clothing fastener
Science and technology Computing
* ZIP (file format), a compressed archive file format
** zip, a command-line program from Info-ZIP
* Zi ...
file formats among others); introduced in PDF 1.2; it can use one of two groups of predictor functions for more compact zlib/deflate compression: ''Predictor 2'' from the TIFF
Tag Image File Format, abbreviated TIFF or TIF, is an image file format for storing raster graphics images, popular among graphic artists, the publishing industry, and photographers. TIFF is widely supported by scanning, faxing, word processin ...
6.0 specification and predictors (filters) from the PNG specification (),
* ''LZWDecode'', a filter based on LZW Compression; it can use one of two groups of predictor functions for more compact LZW compression: ''Predictor 2'' from the TIFF 6.0 specification and predictors (filters) from the PNG specification,
* ''RunLengthDecode'', a simple compression method for streams with repetitive data using the run-length encoding
Run-length encoding (RLE) is a form of lossless data compression in which ''runs'' of data (sequences in which the same data value occurs in many consecutive data elements) are stored as a single data value and count, rather than as the original ...
algorithm and the image-specific filters,
* ''DCTDecode'', a lossy
In information technology, lossy compression or irreversible compression is the class of data compression methods that uses inexact approximations and partial data discarding to represent the content. These techniques are used to reduce data size ...
filter based on the JPEG
JPEG ( ) is a commonly used method of lossy compression for digital images, particularly for those images produced by digital photography. The degree of compression can be adjusted, allowing a selectable tradeoff between storage size and imag ...
standard,
* ''CCITTFaxDecode'', a lossless bi-level (black/white) filter based on the Group 3 or Group 4 CCITT
The ITU Telecommunication Standardization Sector (ITU-T) is one of the three sectors (divisions or units) of the International Telecommunication Union (ITU). It is responsible for coordinating standards for telecommunications and Information Commu ...
(ITU-T) fax compression standard defined in ITU-T T.4 and T.6,
* ''JBIG2Decode'', a lossy or lossless bi-level (black/white) filter based on the JBIG2
JBIG2 is an image compression standard for bi-level images, developed by the Joint Bi-level Image Experts Group. It is suitable for both lossless and lossy compression. According to a press release from the Group, in its lossless mode JBIG2 ty ...
standard, introduced in PDF 1.4, and
* ''JPXDecode'', a lossy or lossless filter based on the JPEG 2000
JPEG 2000 (JP2) is an image compression standard and coding system. It was developed from 1997 to 2000 by a Joint Photographic Experts Group committee chaired by Touradj Ebrahimi (later the JPEG president), with the intention of superseding the ...
standard, introduced in PDF 1.5.
Normally all image content in a PDF is embedded in the file. But PDF allows image data to be stored in external files by the use of ''external streams'' or ''Alternate Images''. Standardized subsets of PDF, including PDF/A
PDF/A is an ISO-standardized version of the Portable Document Format (PDF) specialized for use in the archiving and long-term preservation of electronic documents. PDF/A differs from PDF by prohibiting features unsuitable for long-term archiving, ...
and PDF/X
PDF/X is a subset of the PDF ISO standard. The purpose of PDF/X is to facilitate graphics exchange, and it therefore has a series of printing-related requirements which do not apply to standard PDF files. For example, in PDF/X-1a all fonts need t ...
, prohibit these features.
Text
Text in PDF is represented by ''text elements'' in page content streams. A text element specifies that ''characters'' should be drawn at certain positions. The characters are specified using the ''encoding'' of a selected ''font resource''.
A font object in PDF is a description of a digital typeface
A typeface (or font family) is the design of lettering that can include variations in size, weight (e.g. bold), slope (e.g. italic), width (e.g. condensed), and so on. Each of these variations of the typeface is a font.
There are list of type ...
. It may either describe the characteristics of a typeface, or it may include an embedded ''font file''. The latter case is called an ''embedded font'' while the former is called an ''unembedded font''. The font files that may be embedded are based on widely used standard digital font formats: Type 1 (and its compressed variant CFF), TrueType, and (beginning with PDF 1.6) OpenType
OpenType is a format for scalable computer fonts. It was built on its predecessor TrueType, retaining TrueType's basic structure and adding many intricate data structures for prescribing typographic behavior. OpenType is a registered trademark o ...
. Additionally PDF supports the Type 3 variant in which the components of the font are described by PDF graphic operators.
Fourteen typefaces, known as the ''standard 14 fonts'', have a special significance in PDF documents:
* Times (v3) (in regular, italic, bold, and bold italic)
* Courier (in regular, oblique, bold and bold oblique)
* Helvetica (v3) (in regular, oblique, bold and bold oblique)
* Symbol
A symbol is a mark, sign, or word that indicates, signifies, or is understood as representing an idea, object, or relationship. Symbols allow people to go beyond what is known or seen by creating linkages between otherwise very different conc ...
* Zapf Dingbats
These fonts are sometimes called the ''base fourteen fonts''. These fonts, or suitable substitute fonts with the same metrics, should be available in most PDF readers, but they are not ''guaranteed'' to be available in the reader, and may only display correctly if the system has them installed. Fonts may be substituted if they are not embedded in a PDF.
Within text strings, characters are shown using ''character codes'' (integers) that map to glyphs in the current font using an ''encoding''. There are several predefined encodings, including ''WinAnsi'', ''MacRoman'', and many encodings for East Asian languages and a font can have its own built-in encoding. (Although the WinAnsi and MacRoman encodings are derived from the historical properties of the Windows
Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for serv ...
and Macintosh
The Mac (known as Macintosh until 1999) is a family of personal computers designed and marketed by Apple Inc., Apple Inc. Macs are known for their ease of use and minimalist designs, and are popular among students, creative professionals, and ...
operating systems, fonts using these encodings work equally well on any platform.) PDF can specify a predefined encoding to use, the font's built-in encoding or provide a lookup table of differences to a predefined or built-in encoding (not recommended with TrueType fonts). The encoding mechanisms in PDF were designed for Type 1 fonts, and the rules for applying them to TrueType fonts are complex.
For large fonts or fonts with non-standard glyphs, the special encodings ''Identity-H'' (for horizontal writing) and ''Identity-V'' (for vertical) are used. With such fonts, it is necessary to provide a ''ToUnicode'' table if semantic information about the characters is to be preserved.
Transparency
The original imaging model of PDF was, like PostScript's, ''opaque'': each object drawn on the page completely replaced anything previously marked in the same location. In PDF 1.4 the imaging model was extended to allow transparency. When transparency is used, new objects interact with previously marked objects to produce blending effects. The addition of transparency to PDF was done by means of new extensions that were designed to be ignored in products written to PDF 1.3 and earlier specifications. As a result, files that use a small amount of transparency might view acceptably by older viewers, but files making extensive use of transparency could be viewed incorrectly by an older viewer.
The transparency extensions are based on the key concepts of ''transparency groups'', ''blending modes'', ''shape'', and ''alpha''. The model is closely aligned with the features of Adobe Illustrator version 9. The blend modes were based on those used by Adobe Photoshop
Adobe Photoshop is a raster graphics editor developed and published by Adobe Inc. for Microsoft Windows, Windows and macOS. It was originally created in 1988 by Thomas Knoll, Thomas and John Knoll. Since then, the software has become the indu ...
at the time. When the PDF 1.4 specification was published, the formulas for calculating blend modes were kept secret by Adobe. They have since been published.
The concept of a transparency group in PDF specification is independent of existing notions of "group" or "layer" in applications such as Adobe Illustrator. Those groupings reflect logical relationships among objects that are meaningful when editing those objects, but they are not part of the imaging model.
Additional features
Logical structure and accessibility
A "tagged" PDF (see clause 14.8 in ISO 32000) includes document structure and semantics information to enable reliable text extraction and accessibility
Accessibility is the design of products, devices, services, vehicles, or environments so as to be usable by people with disabilities. The concept of accessible design and practice of accessible development ensures both "direct access" (i. ...
. Technically speaking, tagged PDF is a stylized use of the format that builds on the logical structure framework introduced in PDF 1.3. Tagged PDF defines a set of standard structure types and attributes that allow page content (text, graphics, and images) to be extracted and reused for other purposes.
Tagged PDF is not required in situations where a PDF file is intended only for print. Since the feature is optional, and since the rules for Tagged PDF were relatively vague in ISO 32000-1, support for tagged PDF amongst consuming devices, including assistive technology
Assistive technology (AT) is a term for assistive, adaptive, and rehabilitative devices for people with disabilities and the elderly. Disabled people often have difficulty performing activities of daily living (ADLs) independently, or even with ...
(AT), is uneven as of 2021. ISO 32000-2, however, includes an improved discussion of tagged PDF which is anticipated to facilitate further adoption.
An ISO-standardized subset of PDF specifically targeted at accessibility, PDF/UA
PDF/UA (PDF/Universal Accessibility), formally ISO 14289, is an International Organization for Standardization (ISO) standard for accessible PDF technology. A technical specification intended for developers implementing PDF writing and processing ...
, was first published in 2012.
Optional Content Groups (layers)
With the introduction of PDF version, 1.5 (2003) came the concept of Layers. Layers, or as they are more formally known Optional Content Groups (OCGs), refer to sections of content in a PDF document that can be selectively viewed or hidden by document authors or viewers. This capability is useful in CAD drawings, layered artwork, maps, multi-language documents, etc.
Basically, it consists of an Optional Content Properties Dictionary added to the document root. This dictionary contains an array of Optional Content Groups (OCGs), each describing a set of information and each of which may be individually displayed or suppressed, plus a set of Optional Content Configuration Dictionaries, which give the status (Displayed or Suppressed) of the given OCGs.
Encryption and signatures
A PDF file may be encrypted, for security, in which case a password is needed to view or edit the contents. PDF 2.0 defines 256-bit AES encryption as standard for PDF 2.0 files. The PDF Reference also defines ways that third parties can define their own encryption systems for PDF.
PDF files may be digitally signed, to provide secure authentication; complete details on implementing digital signatures in PDF is provided in ISO 32000-2.
PDF files may also contain embedded DRM
DRM may refer to:
Government, military and politics
* Defense reform movement, U.S. campaign inspired by Col. John Boyd
* Democratic Republic of Madagascar, a former socialist state (1975–1992) on Madagascar
* Direction du renseignement militai ...
restrictions that provide further controls that limit copying, editing or printing. These restrictions depend on the reader software to obey them, so the security they provide is limited.
The standard security provided by PDF consists of two different methods and two different passwords: a ''user password'', which encrypts the file and prevents opening, and an ''owner password'', which specifies operations that should be restricted even when the document is decrypted, which can include modifying, printing, or copying text and graphics out of the document, or adding or modifying text notes and AcroForm fields. The user password encrypts the file, while the owner password does not, instead relying on client software to respect these restrictions. An owner password can easily be removed by software, including some free online services. Thus, the use restrictions that a document author places on a PDF document are not secure, and cannot be assured once the file is distributed; this warning is displayed when applying such restrictions using Adobe Acrobat
Adobe Acrobat is a family of application software and Web services developed by Adobe Inc. to view, create, manipulate, print and manage Portable Document Format (PDF) files.
The family comprises Acrobat Reader (formerly Reader), Acrobat (forme ...
software to create or edit PDF files.
Even without removing the password, most freeware or open source PDF readers ignore the permission "protections" and allow the user to print or make copy of excerpts of the text as if the document were not limited by password protection.
Beginning with PDF 1.5, Usage rights (UR) signatures are used to enable additional interactive features that are not available by default in a particular PDF viewer application. The signature is used to validate that the permissions have been granted by a bona fide
In human interactions, good faith ( la, bona fides) is a sincere intention to be fair, open, and honest, regardless of the outcome of the interaction. Some Latin phrases have lost their literal meaning over centuries, but that is not the case ...
granting authority. For example, it can be used to allow a user:
* To save the PDF document along with a modified form and/or annotation data
* Import form data files in FDF, XFDF, and text (CSV/TSV) formats
* Export form data files in FDF and XFDF formats
* Submit form data
* Instantiate new pages from named page templates
* Apply a digital signature
A digital signature is a mathematical scheme for verifying the authenticity of digital messages or documents. A valid digital signature, where the prerequisites are satisfied, gives a recipient very high confidence that the message was created b ...
to existing digital signature form field
* Create, delete, modify, copy, import, and export annotations
For example, Adobe Systems grants permissions to enable additional features in Adobe Reader, using public-key cryptography
Public-key cryptography, or asymmetric cryptography, is the field of cryptographic systems that use pairs of related keys. Each key pair consists of a public key and a corresponding private key. Key pairs are generated with cryptographic alg ...
. Adobe Reader verifies that the signature uses a certificate
Certificate may refer to:
* Birth certificate
* Marriage certificate
* Death certificate
* Gift certificate
* Certificate of authenticity, a document or seal certifying the authenticity of something
* Certificate of deposit, or CD, a financial pro ...
from an Adobe-authorized certificate authority. Any PDF application can use this same mechanism for its own purposes.
Under specific circumstances including non- patched systems of the receiver, the information the receiver of a digital signed document sees can be manipulated by the sender after the document has been signed by the signer.
PAdES (''PDF Advanced Electronic Signatures'') is a set of restrictions and extensions to PDF and ISO 32000-1 making it suitable for advanced electronic signatures. This is published by ETSI
The European Telecommunications Standards Institute (ETSI) is an independent, not-for-profit, standardization organization in the field of information and communications. ETSI supports the development and testing of global technical standard ...
as TS 102 778.
File attachments
PDF files can have file attachments which processors may access and open or save to a local filesystem.
Metadata
PDF files can contain two types of metadata. The first is the Document Information Dictionary, a set of key/value fields such as author, title, subject, creation and update dates. This is optional and is referenced from Info
key in the trailer of the file. A small set of fields is defined and can be extended with additional text values if required. This method is deprecated in PDF 2.0.
In PDF 1.4, support was added for Metadata Streams, using the Extensible Metadata Platform
The Extensible Metadata Platform (XMP) is an ISO standard, originally created by Adobe Systems Inc., for the creation, processing and interchange of standardized and custom metadata for digital documents and data sets.
XMP standardizes a data ...
(XMP) to add XML standards-based extensible metadata as used in other file formats. PDF 2.0 allows metadata to be attached to any object in the document, such as information about embedded illustrations, fonts, images as well as the whole document (attaching to the document catalog), using an extensible schema.
PDF documents can also contain display settings, including the page display layout and zoom level in a Viewer Preferences object. Adobe Reader uses these settings to override the user's default settings when opening the document. The free Adobe Reader cannot remove these settings.
Accessibility
PDF files can be created specifically to be accessible for people with disabilities. PDF file formats in use can include tags, text equivalents, captions, audio descriptions, and more. Some software can automatically produce tagged PDFs, but this feature is not always enabled by default. Leading screen reader
A screen reader is a form of assistive technology (AT) that renders text and image content as speech or braille output. Screen readers are essential to people who are blindness, blind, and are useful to people who are visual impairment, visually ...
s, including JAWS
Jaws or Jaw may refer to:
Anatomy
* Jaw, an opposable articulated structure at the entrance of the mouth
** Mandible, the lower jaw
Arts, entertainment, and media
* Jaws (James Bond), a character in ''The Spy Who Loved Me'' and ''Moonraker''
* ...
, Window-Eyes
Window-Eyes is a screen reader for the Microsoft Windows operating system, developed by GW Micro. The first version was released in 1995.
Features
Window-Eyes 9.4 is compatible with Windows Vista, Windows Server 2008, Windows 7, Windows 8, and ...
, Hal, and Kurzweil 1000 and 3000 can read tagged PDF. Moreover, tagged PDFs can be re-flowed and magnified for readers with visual impairments. Adding tags to older PDFs and those that are generated from scanned documents can present some challenges.
One of the significant challenges with PDF accessibility is that PDF documents have three distinct views, which, depending on the document's creation, can be inconsistent with each other. The three views are (i) the physical view, (ii) the tags view, and (iii) the content view. The physical view is displayed and printed (what most people consider a PDF document). The tags view is what screen readers and other assistive technologies use to deliver high-quality navigation and reading experience to users with disabilities. The content view is based on the physical order of objects within the PDF's content stream and may be displayed by software that does not fully support the tags' view, such as the Reflow feature in Adobe's Reader.
PDF/UA
PDF/UA (PDF/Universal Accessibility), formally ISO 14289, is an International Organization for Standardization (ISO) standard for accessible PDF technology. A technical specification intended for developers implementing PDF writing and processing ...
, the International Standard for accessible PDF based on ISO 32000-1 was first published as ISO 14289–1 in 2012 and establishes normative language for accessible PDF technology.
Multimedia
''Rich Media PDF'' is a PDF file including interactive content that can be embedded or linked within the file. It can contain images, audio, video content or buttons. For example, if the interactive PDF is a digital catalog for an E-commerce business, products can be listed on the PDF pages, can be added images, links to the website and buttons to order directly from there.
Forms
''Interactive Forms'' is a mechanism to add forms to the PDF file format. PDF currently supports two different methods for integrating data and PDF forms. Both formats today coexist in the PDF specification:
* AcroForms (also known as Acrobat forms), introduced in the PDF 1.2 format specification and included in all later PDF specifications.
* XML Forms Architecture
XFA (also known as XFA forms) stands for XML Forms Architecture, a family of proprietary XML specifications that was suggested and developed by JetForm to enhance the processing of web forms. It can be also used in PDF files starting with the ...
(XFA) forms, introduced in the PDF 1.5 format specification. Adobe XFA Forms are not compatible with AcroForms. XFA was deprecated from PDF with PDF 2.0.
AcroForms were introduced in the PDF 1.2 format. AcroForms permit using objects (''e.g.'' text box
type=search
placeholder=An example text box, which can be used to search the English Wikipedia.
A text box (input box), text field or text entry box is a control element of a graphical user interface, that should enable the user to input ...
es, Radio button
A radio button or option button is a graphical control element that allows the user to choose only one of a predefined set of mutually exclusive options. The singular property of a radio button makes it distinct from checkboxes, where the user ...
s, ''etc.'') and some code (''e.g.'' JavaScript
JavaScript (), often abbreviated as JS, is a programming language that is one of the core technologies of the World Wide Web, alongside HTML and CSS. As of 2022, 98% of Website, websites use JavaScript on the Client (computing), client side ...
). Alongside the standard PDF action types, interactive forms (AcroForms) support submitting, resetting, and importing data. The "submit" action transmits the names and values of selected interactive form fields to a specified uniform resource locator (URL). Interactive form field names and values may be submitted in any of the following formats, (depending on the settings of the action's ExportFormat, SubmitPDF, and XFDF flags):
; HTML Form format: HTML 4.01 Specification since PDF 1.5; HTML 2.0 since 1.2
; Forms Data Format (FDF): based on PDF, uses the same syntax and has essentially the same file structure, but is much simpler than PDF since the body of an FDF document consists of only one required object. Forms Data Format is defined in the PDF specification (since PDF 1.2). The Forms Data Format can be used when submitting form data to a server, receiving the response, and incorporating it into the interactive form. It can also be used to export form data to stand-alone files that can be imported back into the corresponding PDF interactive form. FDF was originally defined in 1996 as part of ISO 32000-2:2017.
; XML Forms Data Format (XFDF): (external XML Forms Data Format Specification, Version 2.0; supported since PDF 1.5; it replaced the "XML" form submission format defined in PDF 1.4) the XML version of Forms Data Format, but the XFDF implements only a subset of FDF containing forms and annotations. Some entries in the FDF dictionary do not have XFDF equivalents – such as the Status, Encoding, JavaScript, Page's keys, EmbeddedFDFs, Differences, and Target. In addition, XFDF does not allow the spawning, or addition, of new pages based on the given data; as can be done when using an FDF file. The XFDF specification is referenced (but not included) in PDF 1.5 specification (and in later versions). It is described separately in ''XML Forms Data Format Specification''. The PDF 1.4 specification allowed form submissions in XML format, but this was replaced by submissions in XFDF format in the PDF 1.5 specification. XFDF conforms to the XML standard. XFDF can be used in the same way as FDF; e.g., form data is submitted to a server, modifications are made, then sent back and the new form data is imported in an interactive form. It can also be used to export form data to stand-alone files that can be imported back into the corresponding PDF interactive form. As of August, 2019, XFDF 3.0 is an ISO/IEC standard under the formal name ''ISO 19444-1:2019 - Document management — XML Forms Data Format — Part 1: Use of ISO 32000-2 (XFDF 3.0)''. This standard is a normative reference of ISO 32000-2.
; PDF
The entire document can be submitted rather than individual fields and values, as was defined in PDF 1.4.
AcroForms can keep form field values in external stand-alone files containing key-value pairs. The external files may use Forms Data Format (FDF) and XML Forms Data Format (XFDF) files. The usage rights (UR) signatures define rights for import form data files in FDF, XFDF and text ( CSV/ TSV) formats, and export form data files in FDF and XFDF formats.
In PDF 1.5, Adobe Systems introduced a proprietary format for forms; Adobe XML Forms Architecture
XFA (also known as XFA forms) stands for XML Forms Architecture, a family of proprietary XML specifications that was suggested and developed by JetForm to enhance the processing of web forms. It can be also used in PDF files starting with the P ...
(XFA). Adobe XFA Forms are not compatible with ISO 32000's AcroForms feature, and most PDF processors do not handle XFA content. The XFA specification is referenced from ISO 32000-1/PDF 1.7 as an external proprietary specification, and was entirely deprecated from PDF with ISO 32000-2 (PDF 2.0).
Licensing
Anyone may create applications that can read and write PDF files without having to pay royalties to Adobe Systems
Adobe Inc. ( ), originally called Adobe Systems Incorporated, is an American multinational computer software company incorporated in Delaware
and headquartered in San Jose, California. It has historically specialized in software for the crea ...
; Adobe holds patents to PDF, but licenses them for royalty-free
Royalty-free (RF) material subject to copyright or other intellectual property rights may be used without the need to pay royalties or license fees for each use, per each copy or volume sold or some time period of use or sales.
Computer standard ...
use in developing software complying with its PDF specification.
Security
In November 2019, researchers from Ruhr University Bochum
The Ruhr University Bochum (, ) is a public research university located in the southern hills of the central Ruhr area, Bochum, Germany. It was founded in 1962 as the first new public university in Germany after World War II. Instruction began in ...
and Hackmanit GmbH published attacks on digitally signed PDFs . They showed how to change the visible content in a signed PDF without invalidating the signature in 21 of 22 desktop PDF viewers and 6 of 8 online validation services by abusing implementation flaws.
At the same conference, they additionally showed how to exfiltrate the plaintext of encrypted content in PDFs. In 2021, they showed new so-called ''shadow attacks'' on PDFs that abuse the flexibility of features provided in the specification. An overview of security issues in PDFs regarding denial of service
In computing, a denial-of-service attack (DoS attack) is a cyber-attack in which the perpetrator seeks to make a machine or network resource unavailable to its intended users by temporarily or indefinitely disrupting services of a host connect ...
, information disclosure
Information is an abstract concept that refers to that which has the power to inform. At the most fundamental level information pertains to the interpretation of that which may be sensed. Any natural process that is not completely random, ...
, data manipulation
Statistics, when used in a misleading fashion, can trick the casual observer into believing something other than what the data shows. That is, a misuse of statistics occurs when a statistical argument asserts a falsehood. In some cases, the misus ...
, and Arbitrary code execution attacks was presented by Jens Müller.
PDF attachments carrying viruses were first discovered in 2001. The virus, named ''OUTLOOK.PDFWorm'' or ''Peachy'', uses Microsoft Outlook
Microsoft Outlook is a personal information manager software system from Microsoft, available as a part of the Microsoft Office and Microsoft 365 software suites. Though primarily an email client, Outlook also includes such functions as Calen ...
to send itself as an attached Adobe PDF file. It was activated with Adobe Acrobat, but not with Acrobat Reader.
From time to time, new vulnerabilities are discovered in various versions of Adobe Reader, prompting the company to issue security fixes. Other PDF readers are also susceptible. One aggravating factor is that a PDF reader can be configured to start automatically if a web page has an embedded PDF file, providing a vector for attack. If a malicious web page contains an infected PDF file that takes advantage of a vulnerability in the PDF reader, the system may be compromised even if the browser is secure. Some of these vulnerabilities are a result of the PDF standard allowing PDF documents to be scripted with JavaScript. Disabling JavaScript execution in the PDF reader can help mitigate such future exploits, although it does not protect against exploits in other parts of the PDF viewing software. Security experts say that JavaScript is not essential for a PDF reader and that the security benefit that comes from disabling JavaScript outweighs any compatibility issues caused. One way of avoiding PDF file exploits is to have a local or web service convert files to another format before viewing.
On March 30, 2010 security researcher Didier Stevens reported an Adobe Reader and Foxit Reader exploit that runs a malicious executable if the user allows it to launch when asked.
Software
Viewers and editors
PDF viewers are generally provided free of charge, and many versions are available from a variety of sources.
There are many software options for creating PDFs, including the PDF printing capabilities built into macOS
macOS (; previously OS X and originally Mac OS X) is a Unix operating system developed and marketed by Apple Inc. since 2001. It is the primary operating system for Apple's Mac computers. Within the market of desktop and lapt ...
, iOS
iOS (formerly iPhone OS) is a mobile operating system created and developed by Apple Inc. exclusively for its hardware. It is the operating system that powers many of the company's mobile devices, including the iPhone; the term also includes ...
, and most Linux
Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, which ...
distributions, LibreOffice, Microsoft Office 2007 (if updated to SP2) and later, WordPerfect 9, Scribus, numerous PDF print drivers for Microsoft Windows
Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for serv ...
, the pdfTeX
__NOTOC__
The computer program pdfTeX is an extension of Knuth's typesetting program TeX, and was originally written and developed into a publicly usable product by Hà n Thế Thà nh as a part of the work for his PhD thesis at the Faculty of In ...
typesetting system, the DocBook PDF tools, applications developed around Ghostscript and Adobe Acrobat
Adobe Acrobat is a family of application software and Web services developed by Adobe Inc. to view, create, manipulate, print and manage Portable Document Format (PDF) files.
The family comprises Acrobat Reader (formerly Reader), Acrobat (forme ...
itself as well as Adobe InDesign
Adobe InDesign is a desktop publishing and page layout designing software application produced by Adobe Inc. and first released in 1999. It can be used to create works such as posters, flyers, brochures, magazines, newspapers, presentations, ...
, Adobe FrameMaker
Adobe FrameMaker is a document processor designed for writing and editing large or complex documents, including structured documents. It was originally developed by Frame Technology Corporation, which was bought by Adobe Systems, Adobe.
Overvie ...
, Adobe Illustrator, Adobe Photoshop
Adobe Photoshop is a raster graphics editor developed and published by Adobe Inc. for Microsoft Windows, Windows and macOS. It was originally created in 1988 by Thomas Knoll, Thomas and John Knoll. Since then, the software has become the indu ...
. Google
Google LLC () is an American multinational technology company focusing on search engine technology, online advertising, cloud computing, computer software, quantum computing, e-commerce, artificial intelligence, and consumer electronics. ...
's online office suite Google Docs
Google Docs is an online word processor included as part of the free, web-based Google Docs Editors suite offered by Google, which also includes: Google Sheets, Google Slides, Google Drawings, Google Forms, Google Sites and Google Keep. Google Do ...
allows for uploading and saving to PDF. Some web apps offer free PDF editing and annotation tools.
The Free Software Foundation
The Free Software Foundation (FSF) is a 501(c)#501(c)(3), 501(c)(3) non-profit organization founded by Richard Stallman on October 4, 1985, to support the free software movement, with the organization's preference for software being distributed ...
once thought of as one of their high priority projects to be "developing a free, high-quality and fully functional set of libraries and programs that implement the PDF file format and associated technologies to the ISO 32000 standard." In 2011, however, the GNU PDF project was removed from the list of "high priority projects" due to the maturation of the Poppler library, which has enjoyed wider use in applications such as Evince
Evince (), also known as GNOME Document Viewer, is a free and open source document viewer supporting many document file formats including PDF, PostScript, DjVu, TIFF, XPS and DVI. It is designed for the GNOME desktop environment.
The develo ...
with the GNOME
A gnome is a mythological creature and diminutive spirit in Renaissance magic and alchemy, first introduced by Paracelsus in the 16th century and later adopted by more recent authors including those of modern fantasy literature. Its characte ...
desktop environment. Poppler is based on Xpdf
Xpdf is a free and open-source PDF viewer for operating systems supported by the Qt toolkit. Versions prior to 4.00 were written for the X Window System and Motif.
Functions
Xpdf runs on nearly any Unix-like operating system. Binaries are als ...
code base. There are also commercial development libraries available as listed in List of PDF software.
The Apache PDFBox
Apache PDFBox is an open source pure-Java library that can be used to create, render, print, split, merge, alter, verify and extract text and meta-data of PDF files.
Open Hub reports over 11,000 commits (since the start as an Apache project) by ...
project of the Apache Software Foundation
The Apache Software Foundation (ASF) is an American nonprofit corporation (classified as a 501(c)(3) organization in the United States) to support a number of open source software projects. The ASF was formed from a group of developers of the A ...
is an open source Java library for working with PDF documents. PDFBox is licensed under the Apache License.
Printing
Raster image processor
A raster image processor (RIP) is a component used in a printing system which produces a raster image also known as a bitmap. Such a bitmap is used by a later stage of the printing system to produce the printed output. The input may be a page de ...
s (RIPs) are used to convert PDF files into a raster format
upright=1, The Smiley, smiley face in the top left corner is a raster image. When enlarged, individual pixels appear as squares. Enlarging further, each pixel can be analyzed, with their colors constructed through combination of the values for ...
suitable for imaging onto paper and other media in printers, digital production presses and prepress in a process known as rasterisation. RIPs capable of processing PDF directly include the Adobe PDF Print Engine from Adobe Systems
Adobe Inc. ( ), originally called Adobe Systems Incorporated, is an American multinational computer software company incorporated in Delaware
and headquartered in San Jose, California. It has historically specialized in software for the crea ...
and Jaws and the Harlequin RIP
"Harlequin (software)" is a raster image processor first released in 1990 under the name ScriptWorks running as a command-line application to render PostScript language files under Unix. It was developed by Harlequin, a software company based in ...
from Global Graphics
Global Graphics PLC is known for its digital printing and document technology including the Harlequin (software company), Harlequin and Jaws Raster image processor, RIPs and the gDoc digital document software. The Company supplies its software und ...
.
In 1993, the Jaws raster image processor
A raster image processor (RIP) is a component used in a printing system which produces a raster image also known as a bitmap. Such a bitmap is used by a later stage of the printing system to produce the printed output. The input may be a page de ...
from Global Graphics
Global Graphics PLC is known for its digital printing and document technology including the Harlequin (software company), Harlequin and Jaws Raster image processor, RIPs and the gDoc digital document software. The Company supplies its software und ...
became the first shipping prepress RIP that interpreted PDF natively without conversion to another format. The company released an upgrade to their Harlequin RIP with the same capability in 1997.
Agfa-Gevaert introduced and shipped Apogee, the first prepress workflow system based on PDF, in 1997.
Many commercial offset printers have accepted the submission of press-ready PDF files as a print source, specifically the PDF/X-1a subset and variations of the same. The submission of press-ready PDF files is a replacement for the problematic need for receiving collected native working files.
In 2006, PDF was widely accepted as the standard print job format at the Open Source Development Labs
Open Source Development Labs (OSDL) was a non-profit organization supported by a consortium to promote Linux for enterprise computing. Founded in 2000, OSDL positioned itself as an independent, non-profit lab for developers who are adding enterpris ...
Printing Summit. It is supported as a print job format by the Common Unix Printing System
CUPS (formerly an acronym for Common UNIX Printing System) is a modular printing system for Unix-like computer operating systems which allows a computer to act as a print server. A computer running CUPS is a host that can accept print jobs f ...
and desktop application projects such as GNOME
A gnome is a mythological creature and diminutive spirit in Renaissance magic and alchemy, first introduced by Paracelsus in the 16th century and later adopted by more recent authors including those of modern fantasy literature. Its characte ...
, KDE
KDE is an international Free software movement, free software community that develops free and open-source software. As a central development hub, it provides tools and resources that allow collaborative work on this kind of software. Well-know ...
, Firefox, Thunderbird, LibreOffice and OpenOffice have switched to emit print jobs in PDF.
Some desktop printers also support direct PDF printing, which can interpret PDF data without external help.
Native display model
PDF was selected as the "native" metafile format for Mac OS X
macOS (; previously OS X and originally Mac OS X) is a Unix operating system developed and marketed by Apple Inc. since 2001. It is the primary operating system for Apple's Mac (computer), Mac computers. Within the market of ...
, replacing the PICT format of the earlier classic Mac OS
Mac OS (originally System Software; retronym: Classic Mac OS) is the series of operating systems developed for the Macintosh family of personal computers by Apple Computer from 1984 to 2001, starting with System 1 and ending with Mac OS 9. The ...
. The imaging model of the Quartz
Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical form ...
graphics layer is based on the model common to Display PostScript and PDF, leading to the nickname ''Display PDF''. The Preview application can display PDF files, as can version 2.0 and later of the Safari
A safari (; ) is an overland journey to observe wild animals, especially in eastern or southern Africa. The so-called "Big Five" game animals of Africa – lion, leopard, rhinoceros, elephant, and Cape buffalo – particularly form an importa ...
web browser. System-level support for PDF allows Mac OS X applications to create PDF documents automatically, provided they support the OS-standard printing architecture. The files are then exported in PDF 1.3 format according to the file header. When taking a screenshot under Mac OS X versions 10.0 through 10.3, the image was also captured as a PDF; later versions save screen captures as a PNG file, though this behavior can be set back to PDF if desired.
Annotation
Adobe Acrobat
Adobe Acrobat is a family of application software and Web services developed by Adobe Inc. to view, create, manipulate, print and manage Portable Document Format (PDF) files.
The family comprises Acrobat Reader (formerly Reader), Acrobat (forme ...
is one example of proprietary software that allows the user to annotate, highlight, and add notes to already created PDF files. One UNIX application available as free software
Free software or libre software is computer software distributed under terms that allow users to run the software for any purpose as well as to study, change, and distribute it and any adapted versions. Free software is a matter of liberty, no ...
(under the GNU General Public License
The GNU General Public License (GNU GPL or simply GPL) is a series of widely used free software licenses that guarantee end users the Four Freedoms (Free software), four freedoms to run, study, share, and modify the software. The license was th ...
) is PDFedit
PDFedit is a free PDF editor for Unix-like operating systems (including Cygwin on top of Windows). It does not support editing protected or encrypted PDF files or word processor-style text manipulation, however.freeware
Freeware is software, most often proprietary, that is distributed at no monetary cost to the end user. There is no agreed-upon set of rights, license, or EULA that defines ''freeware'' unambiguously; every publisher defines its own rules for the f ...
Foxit Reader, available for Microsoft Windows
Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for serv ...
, macOS
macOS (; previously OS X and originally Mac OS X) is a Unix operating system developed and marketed by Apple Inc. since 2001. It is the primary operating system for Apple's Mac computers. Within the market of desktop and lapt ...
and Linux
Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, which ...
, allows annotating documents. Tracker Software's PDF-XChange Viewer allows annotations and markups without restrictions in its freeware alternative. Apple
An apple is an edible fruit produced by an apple tree (''Malus domestica''). Apple fruit tree, trees are agriculture, cultivated worldwide and are the most widely grown species in the genus ''Malus''. The tree originated in Central Asia, wh ...
's macOS
macOS (; previously OS X and originally Mac OS X) is a Unix operating system developed and marketed by Apple Inc. since 2001. It is the primary operating system for Apple's Mac computers. Within the market of desktop and lapt ...
's integrated PDF viewer, Preview, does also enable annotations as does the open-source software Skim, with the latter supporting interaction with LaTeX
Latex is an emulsion (stable dispersion) of polymer microparticles in water. Latexes are found in nature, but synthetic latexes are common as well.
In nature, latex is found as a milky fluid found in 10% of all flowering plants (angiosperms ...
, SyncTeX, and PDFSync and integration with BibDesk
BibDesk is an open-source reference management software package for macOS, used to manage bibliographies and references when writing essays and articles. It can also be used to organize and maintain a library of documents in PDF format and other f ...
reference management software. Freeware Qiqqa
Qiqqa (pronounced "Quicker") is a free and opensource software that allows researchers to work with thousands of PDFs. It combines PDF reference management tools, a citation manager, and a mind map brainstorming tool. It integrates with Microsoft ...
can create an annotation report that summarizes all the annotations and notes one has made across their library of PDFs. The Text Verification Tool exports differences in documents as annotations and markups.
There are also web annotation systems that support annotation in pdf and other documents formats. In cases where PDFs are expected to have all of the functionality of paper documents, ink annotation is required.
Alternatives
The Open XML Paper Specification
Open XML Paper Specification (also referred to as OpenXPS) is an open specification for a page description language and a fixed-document format. Microsoft developed it as the XML Paper Specification (XPS). In June 2009, Ecma International adopt ...
is a competing format used both as a page description language and as the native print spooler format for Microsoft Windows
Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for serv ...
since Windows Vista
Windows Vista is a major release of the Windows NT operating system developed by Microsoft. It was the direct successor to Windows XP, which was released five years before, at the time being the longest time span between successive releases of ...
.
Mixed Object: Document Content Architecture is a competing format. MO:DCA-P is a part of Advanced Function Presentation
Advanced Function Presentation (AFP) is a presentation architecture and family of associated printer software and hardware that provides for document and information presentation independent of specific applications and devices.
Using AFP, users c ...
.
See also
* Web document
* XSL Formatting Objects
References
Further reading
*
* PDF 2.0
* PDF 2.0
PDF 1.7 (ISO 32000-1:2008)
PDF 1.7
an
errata to 1.7
PDF 1.6
() an
errata to 1.6
PDF 1.5
an
errata to 1.5
PDF 1.4
() an
errata to 1.4
PDF 1.3
() an
errata to 1.3
External links
PDF Association
– The PDF Association is the industry association for software developers producing or processing PDF files.
Adobe: PostScript vs. PDF
– Official introductory comparison of PS, EPS vs. PDF.
* – Information about PDF/E and PDF/UA specification for accessible documents file format (archived by The Wayback Machine
The Wayback Machine is a digital archive of the World Wide Web founded by the Internet Archive, a nonprofit based in San Francisco, California. Created in 1996 and launched to the public in 2001, it allows the user to go "back in time" and see ...
)
PDF/A-1 ISO standard
published by the International Organization for Standardization
The International Organization for Standardization (ISO ) is an international standard development organization composed of representatives from the national standards organizations of member countries. Membership requirements are given in Ar ...
(with corrigenda)
PDF Reference and Adobe Extensions to the PDF Specification
– Introduction to PDF vs. PostScript and PDF internals (up to v1.3)
The Camelot Paper
– the paper in which John Warnock outlined the project that created PDF
Everything you wanted to know about PDF but was afraid to ask
â€
recording of a talk by Leonard Rosenthol
(45 mins) (Adobe Systems
Adobe Inc. ( ), originally called Adobe Systems Incorporated, is an American multinational computer software company incorporated in Delaware
and headquartered in San Jose, California. It has historically specialized in software for the crea ...
) at TUG 2007
{{Authority control
Computer-related introductions in 1993
Adobe Inc.
Digital press
Electronic documents
Graphics file formats
ISO standards
Office document file formats
Open formats
Page description languages
Vector graphics